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   "description": "This Digital Terrain Model (DTM) data was produced all or in part from LiDAR information as of 2014. The LiDAR derived DTM covers Will County, Illinois and include inland streams, rivers, lakes ponds and tidal features. These data are appropriate for use in local and regional analysis. This dataset was contracted as 1 ppsm LiDAR point cloud data, however the data delivered was 2 ppsm and thus so are the derivative models of Will County, Illinois. Will County is approximately 849 square miles in north eastern Illinois. Data was collected at a nominal pulse spacing (NPS) of 0.7 meter. Data acquisition, processing and assessment is compliant with procedures and methods stated in U.S. Geological Survey National Geospatial Program LiDAR Base Specification Version 1.0 and Federal Emergency Management Agency Procedure Memorandum 61.Digital Elevation Models (including terrain and surface models) are raster data sets created from whole LiDAR point cloud data sets (LAS files). The LAS files are the standard LiDAR file format which contains the raw point cloud data, these data are normally classified and distinguished between points on the ground, water or elevated features such as buildings, trees, towers, bridges, etc.. These LAS files are processed into elevation models to create gridded rasters. The first returns can be used to map the top reflective surface (Digital Surface Models - DSM), these normally include open terrain areas, as well as the tops of buildings, trees, towers, and other features elevated above the bare earth. The last returns are used to map the bare-earth terrain (Digital Terrain Models - DTM), these are normally produced with irregularly-spaced points rather than the uniform grid structure of a Digital Elevation Model (DEM), Digital Terrain Models will often include breaklines to help define edges of water bodies.",
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   "description": "Product: These lidar data are processed Classified LAS 1.4 files, formatted to 10097 individual 2000 foot x 2000 foot tiles; used to create intensity images, 3D breaklines and hydro-flattened DEMs as necessary. Geographic Extent: Grundy, Kendall, and DeKalb County, Illinois, covering approximately 1,388 square miles. Grundy, Kendall, and DeKalb Counties are one area of interest (AOI) from a lidar survey that was collected over two (2) areas of interest in Illinois identified as LaSalle and Expansion Counties. LaSalle and Expansion Counties cover a total of approximately 2,563 square miles. Dataset Description: Grundy, Kendall, and DeKalb Counties, Illinois 2017 Lidar project called for the Planning, Acquisition, processing and derivative products of lidar data to be collected at a nominal pulse spacing (NPS) of 0.7 meter. Project specifications are based on the U.S. Geological Survey National Geospatial Program Base Lidar Specification, Version 1.2; Quality Level 2. The data was developed based on a horizontal projection/datum of NAD83 (2011), State Plane Coordinate System Illinois East (FIPS 1201), US Survey Feet and vertical datum of NAVD88 (GEOID12B), US Survey Feet. Lidar data was delivered as flightline-extent unclassified LAS swaths, as processed Classified LAS 1.4 files, formatted to 10097 individual 2000 foot x 2000 foot tiles, as tiled Intensity Imagery, and as tiled bare earth DEMs; all tiled to the same 2000 foot x 2000 foot schema. Ground Conditions: Lidar was collected in November 2017, due to an isolated anomaly found in the the lidar data in LaSalle County one re-flight was flown in April 2018, while no snow was on the ground and rivers were at or below normal levels. A Low Confidence polygon was use to circumscribe an area where lidar was reflected by particulates in smoke stack emission. Photons were unable to penetrate through the emissions for collection of ground surface within the polygon. The emission cloud obscures approximately 3.72 acres of ground surface. Tiles in which the emission cloud occurred are 99101727 and 99301727. In order to post process the lidar data to meet task order specifications and meet ASPRS vertical accuracy guidelines, GRW Aerial Surveys, Inc. established a total of 53 ground control points of which 50 were used to calibrate the lidar to known ground locations established throughout the LaSalle and Expansion Counties project areas. An additional 157 independent accuracy checkpoints, 89 in Bare Earth and Urban landcovers (89 NVA points), 68 in tall Grass/tall weeds/crops, Brush lands/short trees, Forested categories (68 VVA points), were used to assess the vertical accuracy of the data of the entire project area. These checkpoints were not used to calibrate or post process the data.",
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